Such relations are known as superconvergence relations [1]}, or dispersive sum rules [2]}.
We follow the latter terminology and consider the following integrals
\(B_k^+(s) &=\oint _{\infty } {d t \over 2 \pi i} \mathcal {M} (s,t) {1 \over t} {1 \over (t (s+t))^{k} } = 0 \, , \hspace{42.67912pt}k \ge 2 \,,\) 
